1. Field of the Invention
The present invention relates to a magnetic recording medium which has a recording layer formed in a concavo-convex pattern.
2. Description of the Related Art
Conventionally, a magnetic recording medium such as a hard disc has been significantly increased in areal density by means of improvement such as fining magnetic particles forming a recording layer, material changes, and increased precision in the processing of heads. Further increase in the areal density is expected in the future.
However, problems such as a limitation in the processing of the head, side fringes due to the spread of a magnetic field, and crosstalk have become revealed, so that improvements in the areal density by a conventional improvement method has reached their limitations. Thus, a magnetic recording medium such as a discrete track medium and a patterned medium has been proposed as a candidate for a magnetic recording medium which can realize further increase in the areal density (refer to, for example, Japanese Patent Laid-Open Publication No. Hei 9-97419). In such a magnetic recording medium, a recording layer is formed in a predetermined concavo-convex pattern.
Namely, since information is recorded on convex portions of the concavo-convex pattern, it is possible to restrain a side fringe, crosstalk, and the like between a convex portion and another convex portion adjacent thereto. Forming the recording layer in the concavo-convex pattern also has the effect of preventing a magnetic head from adhering to the surface of the magnetic recording medium.
When the surface of the medium is in the concavo-convex pattern, on the other hand, there are cases where recording and reproducing characteristics become worse because of the instability of the flying height of the head. Accordingly, it is considered to deposit a non-magnetic material over the recording layer in the concavo-convex pattern for the purpose of filling concave portions with the non-magnetic material. Then, an excess part of the non-magnetic material above the recording layer is removed to flatten the surface of the magnetic recoding layer.
A method of dry etching is available as a method for processing the recording layer into the concavo-convex pattern. A deposit technology such as sputtering, which is used in the field of semiconductor manufacturing, is available as a method for depositing the non-magnetic material. Also, a processing technology such as CMP (chemical mechanical polishing), which is used in the field of semiconductor manufacturing, is available as a method for removing the excess part of the non-magnetic material above the recording layer to flatten the surface.
It is difficult, however, to completely flatten the surface even if the CMP method or the like is used. A concavo-convex shape in which the concavo-convex pattern of the recording layer is reflected is formed in the surface. In the CMP method, for example, it is difficult to precisely control the amount (thickness) of processing in the order of nanometers. Thus, there are cases where after the non-magnetic material above the recording layer is removed, a part of the recording layer is removed together with the non-magnetic material, and hence difference in the height of the concavo-convex shape in the surface, in which the concavo-convex pattern of the recording layer is reflected, contrarily increases due to difference in the speed of processing of both.
There are cases that the stable flying characteristics of the head cannot be obtained due to such a concavo-convex shape in the surface.